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Austin area backflow devices

I am planning to attempt my first system, I am confused about backflow. My local codes say that control valves with backflow control in them will work. But with lawn and flower bed zones up to 6 or so, and no back flow valves being cheaper. Is it easier and cheaper to run a single backflow devise in my feed line, or seperate valves with backflow built in? What is the norm for central Tx ?

Values with backflow build in contain an AVB - an atmosphiric vacuum breaker. The AVB is connected to the valve just after the valve. These valves MUST be installed such that the valve is 12" higher than the highest outlet the valve supplies. So if you have a hill and you want to install AVBs at the bottom of the hill, no dice.

Similar to an AVB is a PVB - pressure vacuum breaker. In concept, it is similar to the AVB as it too must be installed above all outlets, however the PVB is installed BEFORE the valves, and therefore a single PVB can protect multiple valves.

The next thing is a duel check back-flow assymbly . It's basically a duel check valve with test cocks installed to test the effectiveness of the check valves. Because back-flow is prevented by spring loaded check valves, a duel check can be installed just about anywhere as they don't release anything and they don't have to located above or below valves and irrigation outlets. But they are also considered the least safe. The reason is that all it takes is a stick or other dirt/debrie (that does get in even city water) to get lodged in the check valves basiclly making them stick open rendering them useless.

The mother of all backflows is the RPZ (reduced pressure zone). Similar to the DC, an RPZ can be installed just about anywhere relative to valves and outlets. But in failure mode, the RPZ spews water out rather than allowing it to backflow. So an RPZ generally can NOT be installed indoors nor can it be installed in a pit or meter box because if the RPZ becomes submerged, it can fail to properly prevent backflow. When installed correctly, RPZs are so safe that even when connected with a potable water source, you can safely pump chemicals into the irrigation lines (and RPZs are required if you plan to use fertigation... injecting fertilizer into the irrigation system). The down side to RPZs is that they work my making sure to maintain about a 10 to 15 psi pressure differential between the input and output. If you are in a location where water pressure is low (relative to what is needed for irrigation) and RPZ is going to suck away a good percentage of what available pressure there is.

I believe that you meant to say double check instead of duel check valve. Two way different horses.

Mick

I guessing that you are pointing out that "official" plumbing terminology tries to differentiate between the device known as a "duel check" (which is a device that consists of just two check valves back-to-back) and a "double check backflow preventer" (which is a device that consists of two check valves back-to-back between two shutoff valves, with test cock beteween these components allowing the operation of the two check valves to be tested independantly of each other).

But in some circles, words "duel check" and "double check" improperly get used interchangably (tomato / tamoto).

I initially learned most of what I know about irrigation at www.irrigationtutorials.com, and the irrigation egineer there tries to explain the difference between "duel" and "double". IMHO, his text is a bit confusing. So I try to focus on the test cocks to differentiate between the two devices rather than on a name.

I guessing that you are pointing out that "official" plumbing terminology tries to differentiate between the device known as a "duel check" (which is a device that consists of just two check valves back-to-back) and a "double check backflow preventer" (which is a device that consists of two check valves back-to-back between two shutoff valves, with test cock beteween these components allowing the operation of the two check valves to be tested independantly of each other).

But in some circles, words "duel check" and "double check" improperly get used interchangably (tomato / tamoto).

I initially learned most of what I know about irrigation at www.irrigationtutorials.com, and the irrigation egineer there tries to explain the difference between "duel" and "double". IMHO, his text is a bit confusing. So I try to focus on the test cocks to differentiate between the two devices rather than on a name

No HooKooDooKu, Plumbing Terminology doesn't try to differentiate between the two. It does differentiate between the two with the correct terminology. You might not understand the terminology, or it's use, but it is laid out in those specific terms to be understood, differentiated and carried out in a clear precise manner.

In the twelve general methods for backflow control, the Double Check Valve Assembly (DCVA) is rated as third. The Dual Check Valve Device (DuC or DuCF) is rated as eighth in protection value.

You had said that the Irrigation Engineer confused you with the explanation. So you now use the wrong terms with a little disclaimer about testcocks? Do you think that the uneducated (who are asking for help) will actually notice the part about the testcocks, or will they notice the part about the name?

If you are confused about something, then you might want to think about getting some information and/or training.

Because you actually acknowledge that other people are using the terminology incorrectly is even worse. If you didn't know the correct terms I could understand a mistake.

Early in my career, I also picked up some opinions and pointers from publications and learned from some of the best. But what I also did was to get professional training, learned code, spoke to and consulted with manufacturers, received training and certification in areas including being a Certified Backflow Assembly Tester. If you are confused, please get more information.

These are two completely separate and distinct pieces of plumbing/irrigation hardware. They are not legal or interchangeable for installation in all areas. Check with your Water Purveyor or your Municipality to see what is actually required to satisfy your by-law requirements.